P1244: ROLE OF SELECT T HELPER CELL MONONUCLEAR CELL SUBSETS PROMOTING EPSTEIN-BARR VIRUS-DRIVEN LYMPHOPROLIFERATIVE DISEASE IN THE HU-PBL-SCID MODEL
Authors: E. H. Ahmed, M. Lustberg, C. Hale, S. Sloan, C. Mao, X. Zhang, H. G. Ozer, S. Schlotter, F. Jeney, W. Chan, B. Harrington, C. Weigel, L. Alinari, C. Oakes, T. Abebe, G. K. Behbehani, P. Shindiapina, M. A. Caligiuri, R. A. Baiocchi
Journal: HemaSphere (2022)

Background: The Epstein-Barr virus (EBV) is a gamma herpes virus that infects over 90% of the adult population worldwide. EBV is trophic to human B-cells and is capable of driving benign (mononucleosis) or malignant B-cell lymphoproliferative disorder (EBV-LPD). Infected B-cells are cleared by a highly efficient, EBV-specific, memory cytotoxic T lymphocyte (CTL) response in immunocompetent individuals. EBV ultimately assumes latency and establishes life-long persistence in the memory B-cell compartment. EBV can reactivate a lytic cycle program leading to the production of infectious virus, placing immunocompromised individuals, including HIV patients, organ transplant recipients, and patients with primary immune deficiency at the highest risk for EBV-LPD. Despite the ubiquity of EBV, a small percentage of immunocompromised patients (2-20%) develop EBV-LPD. Such clinical heterogeneity may reflect the presence of host factors that predispose certain individuals to EBV-LPD. Engraftment of severe combined immune deficient (SCID) mice with peripheral blood leukocytes (PBMCs) from EBV seropositive donors leads to spontaneous EBV-LPD of human B-cell origin. PBMCs from EBV+ human donors show distinct rates of EBV-LPD in the Hu-PBL-SCID model. Of all EBV seropositive PBMC donors, only about 20% of donors will induce EBV-LPD in 100% of engrafted mice (High-Incidence, HI donors) and another 20% of donors will never generate EBV-LPD (No-Incidence, NI donors). Development of spontaneous EBV-LPD in the Hu-PBL-SCID model displays an absolute requirement for autologous CD4+ T cells in engrafted PBMC. Aims: Here we aimed to identify immune factors that contribute to the development EBV-LPD in the hu-PBL-SCID model. We hypothesized that distinct phenotypes of PBMCs from HI and NI exist and that specific subsets of mononuclear cells promote EBV-LPD in this model. Methods: To address this hypothesis, we studied a pool of EBV seropositive donors (HI donor n= 4; NI Donor n=5). Results: Immunophenotypic analysis of CD4+ T-helper cell subsets showed HI donors have higher basal levels of T follicular helper (Tfh) and regulatory T-cells (Treg) cells compared to NI donors (p-values = 0.0499 and 0.0309 respectively). Mice engrafted with PBMC depleted of Tfh or Treg subsets from HI donors showed improved survival compared to mice engrafted with non-depleted PBMC. Furthermore, mass-cytometry analysis revealed a significantly higher percentage of myeloid cells in the PBMCs of HI donors compared to NI donors (p-value = 0.0018). Further analysis confirmed a higher percentage of myeloid-derived suppressor cells in the PBMCs of HI donors that, in in vitro EBV-LCL co-cultures, prevented memory CTL proliferation. Summary/Conclusion: Our findings point toward potential immune cell subsets that contribute to the development of EBV-LPD. Further studies will enable us to define immune profile characteristics associated with a high risk of EBV-LPD and point toward potential strategies to prevent these disorders in select patient populations.